Experimental investigation of heat transfer enhancement in heat exchanger due to air bubbles injection

The present work experimentally investigated air bubbles injection on heat transfer enhancement and pressure drop of turbulent flow in two helical coils heat exchanger. The experience is accomplished for turbulent flow with Reynolds number (Re) of (9000 to 50000) for hot water and constant mass flow rate of cold water 0.0331 kg/s .Air bubbles injection in hot water in the range of (1.5, 2.5, and 3.5) lit/min. Experimental results represented by Nusselt number(NU), effectiveness (ε), number of thermal units (NTU) and exergy losses. It was evinced that, the presence of air bubbles in hot water causes enhanced in Nusselt number from (64 to 126) % and increased the friction factor from (66 to 85) % in the Reynolds number range from (9000 to 50000). Bubbles injection has a positive effect on enhanced heat transfer and negative effect of increased friction factor and this represent by thermal enhancement factor which was increased about (1.13 to 1.29) in mass flow rate of hot water of 0.0163 kg/s by using values of air bubbles from (1.5 to 3.5) lit/min. A quantity of number of thermal units (NTU) and effectiveness (ε) appreciably enhanced due to air bubbles. Furthermore, exergy loss with air bubbles was higher than without air bubble injection.